In current digital display systems, field sequential color techniques are often used in producing color images. Light beams in a set of primary colors such as red, green and blue, are sequentially directed at a spatial light modulator during a particular time period, such as a video frame period or a fraction of a video frame period. Accordingly, image data corresponding to each color is sequentially loaded into the spatial light modulator so as to produce color images when the frequency with which the colors are cycles is high enough that the observer's eye cannot readily distinguish the individual color fields. The success of the color image production depends upon the synchronization of the timing of the primary color illumination and the loading of the corresponding image data onto the SLM.
An approach to such synchronization is the use of a photo-detector that detects the phase of a color wheel as shown in FIG. 1. Referring to FIG. 1, color wheel 24 comprises separate color segments, for example red, green and blue. Light source 20 projects a light beam through the color wheel and one or more optical elements (not shown) onto spatial light modulator 26, such as a LCD, LCOS or micromirror based spatial light modulator. As the color wheel rotates at a particular speed, the light beam sequentially illuminates the SLM with a sequence of colored light beams. The position of the color wheel is detected by photo-detector 22. For example, an index mark is made on the color wheel and rotated along with the color wheel. Through the detection of the color index mark by the photo-detector, the positions of the color segments and thus the timing of the color segments passing through the path of the light beam can be determined. Image data corresponding to the color of the illumination incident on the SLM are loaded into the spatial light modulator to produce the color image.
In order to precisely detect the timing of the respective colors, the position of the color index mark on the color wheel needs to be precisely determined, and the relative position of the photo-detector and the color wheel has to be secured. All these require extensive efforts in, for example, aligning the color index mark to the color wheel, and positioning the photo-detector properly.
Therefore, what is desired is a method and apparatus for synchronizing the color fields with the operations of the display system.